The quality of the drinking water supply has become more important with Hungary's entry into the European Community. In some regions of the country, similar to many parts of the world, arsenic removal from drinking water is an urgent task to supply water with an arsenic content under 10 mug/l. We have worked out a new technology for arsenic removal using a membrane technique. Measurements on site were performed in a pilot plant with equipped with a pre-treatment system and a ZW-1000 (Zenon) membrane module. Be-fore expanding the technological process, experiments on laboratory scale were done to find out which kind of pre-treatment and membrane configuration are needed. These experiments were performed with water from deep wells, among them with a high arsenic concentration (200-300 mug/l). The steps of the pre-treatment process were: oxidation with potassium permanganate (KMnO4), coagulation with ferrous(III) sulphate (Fe-2(SO4)(3)), fast mixing of chemicals with a mixer, coagulation with slow mixing and settlement. Following membrane separation, the arsenic concentration was under the permitted value (10 mug/l). Results of experiments on site proved that the new technology was successful and is suitable to produce drinking water at the required quality from raw water with a high arsenic content in a pilot plant.